Brian Hook, an outspoken critic of President Donald Trump, has been hired to be the state department’s director of policy planning, according to a report published Friday by The Daily Caller.

The policy planning director is a critical role in the state department. Foreign Policy, an online magazine which first reported Hook was in line for the position, describes the job as the “strategic brain trust” for Secretary of State Rex Tillerson.

Hook will have direct access to Tillerson, and will be in charge of key specialists and academics in the department. In the past, policy planning directors have been put in charge of everything from crisis management to long-term strategic planning.

“This has the potential to be a very powerful position under Tillerson,” an unnamed GOP Senate aide told Foreign Policy. “It’s a chief adviser position for someone who’s going to need help navigating the building.”

Hook previously served as assistant secretary of state and senior adviser to the United Nations ambassador under President George W. Bush’s administration. He later served as a foreign policy adviser for Mitt Romney during his 2012 bid for presidency.

More recently, Hook gained notoriety within the Trump camp by co-founding the John Hay Initiative, a group that distributed a letter signed by 121 GOP national security experts last March refusing to support Trump’s presidential campaign due to concerns he would “act in ways that would make America less safe.”

Hook did not sign the letter himself, but he made it clear in interviews he was not a Trump supporter.

“Even if you say you support him as the nominee, you go down the list of his positions and you see you disagree on every one,” Hook told Politico during the primaries,

Among Hook’s concerns about then-candidate Trump were his soft stance on Russia and view that NATO was “obsolete.”

Hook co-authored a book last year hailing NATO as the “bedrock of European security” and a key deterrent against “Russian aggression.”

“I’m so disappointed about all the neoconservatives trickling into administration,” a Trump-appointed State Department official told the Daily Caller.

Daniel DePetris, a contributor to The National Interest magazine, tried to sound the alarm last month when rumors circulated about Hook joining the state department.

“Trump should know what he’s getting himself into: if he hires Brian Hook, he will be opening his arms to a member of the very establishment he campaigned against,” DePetris wrote. “He should expect Hook, a career foreign-policy professional, to lobby for courses of action that Trump and his senior White House staff might ordinarily recoil at.”

Despite fierce criticism against Hook, a combination of him being described as a favorite of Tillerson and reports of the Trump administration having a difficult time filling empty positions are believed to be among the key factors that allowed him to land the job.